1. Field of the Disclosure
The present subject matter is generally directed to mobile drilling rig assemblies, and in particular, to a substructure of a mobile drilling rig having telescoping substructure boxes to facilitate drilling rig assembly and erection.
2. Description of the Related Art
In many land-based oil and gas drilling operations, drilling rigs are delivered to an oilfield drilling site by transporting the various components of the drilling rig over roads and/or highways. Typically, the various drilling rig components are transported to a drilling site on one or more truck/trailer combinations, the number of which may depend on the size, weight, and complexity of the rig. Once at the drilling site, the drilling rig components are then assembled, and the drilling rig assembly is raised to an operating position so as to perform drilling operations. After the completion of drilling operations, the mobile drilling rig is then lowered, disassembled, loaded back onto truck/trailer combinations, and transported to a different oilfield drilling site for new drilling operations. Accordingly, the ease with which the various drilling rig components can be transported, assembled and disassembled, and raised and lowered can be a substantial factor in the drilling rig design, as well as the rig's overall operational capabilities and cost effectiveness.
As drilling rig technologies have progressed, the size and weight of mobile drilling rigs has significantly increased so as to meet the higher drilling load capabilities that are oftentimes required to drill deeper wells, particularly in more mature oilfield formations. For example, it is not uncommon for many land-based mobile drilling rigs to have a 1500-2000 HP capability, with hook load capacities of 1 million pounds or greater. Additionally, there are some even larger 3000 HP mobile drilling rigs in operation, with hook and/or rotary load capacities exceeding 1.5 million pounds.
However, as the capacity—and the overall size and weight—of mobile drilling rigs increases, the size and weight of many of the various components of the rig also proportionately increase, a situation that can sometimes contribute to an overall reduction in at least some of the “mobility” characteristics of the rig. For example, a typical drawworks for a 2000 HP mobile rig may weigh in the range of 80-100 thousand pounds, or even more. Furthermore, individual sections of a drilling rig mast may be 30-40 feet or more in length, and may weigh 20-80 thousand pounds each. In many cases, such large and heavy components require the use of a suitably sized crane so as to lift and position the various drilling components during rig assembly. Accordingly, while each of the various larger rig components may be “transportable” over roads and/or highways from one oilfield drilling site to another, the overall logistical considerations for using at least some higher capacity mobile drilling rigs, e.g., 1500 HP and greater, may need to include having a crane present at a given drilling site prior to the commencement of drilling operations in order to facilitate initial rig assembly. Furthermore, a crane may also need to be present after the completion of drilling operations so as to facilitate rig disassembly for transportation to other oilfield drilling sites. As may be appreciated, the requirement that a crane be used during these assembly/disassembly stages can have a significant impact on the overall cost of the drilling operation, as well as the amount of time that may be needed to perform the operations.
In some applications, drilling operations at a given oilfield drilling site may involve drilling a plurality of relatively closely spaced wellbores, sometimes referred to as “pad” drilling. In pad drilling, the distance between adjacent wellbores may be as little as 20-30 feet, or even less, and are oftentimes arranged in a two-dimensional grid pattern, such that rows and columns of wellbores are disposed along lines that run substantially parallel to an x-axis and a y-axis, respectively. In such pad drilling applications, after drilling operations have been completed at one wellbore, it is necessary to move the drilling rig to an adjacent wellbore, which can be quite costly and time consuming when a crane is required to disassemble, lift, and move the various drilling rig components to the next wellbore location before drilling operations can commence. Furthermore, even when the fully assembled and erected drilling rig is designed to be moved from wellbore to wellbore via wheeled trailers or dollies, such moving devices are generally only capable of being moved substantially along a single axis, e.g., along an x-axis or along a y-axis. Accordingly, while it may be feasible to trailer such a mobile drilling rig in an axial direction between closely-spaced adjacent wellbores that are disposed along the same column or row of wellbores making up the grid pattern at a given pad drilling site, it is generally not possible to move the mobile drilling rig laterally or longitudinally, e.g., from row to row or from column to column, when using conventional wheeled trailers or dollies.
Accordingly, there is a need to develop and implement new designs and methods for facilitating the assembly of modern mobile drilling rigs having higher operating capacities without relying on the use of a crane to facilitate the assembly and/or disassembly the rig. Furthermore, there is also a need to facilitate the movement of fully assembled and erected mobile drilling rigs between closely-spaced adjacent wellbores during pad drilling operations. The following disclosure is directed to the design and use of mobile drilling rigs that address, or at least mitigate, at least some of the problems outlined above.